There is a conventionally proposed principle of a compressing mechanism which includes a rotary cylinder having a groove, and a piston slidable within the groove, so that the rotary cylinder is rotated in accordance with the movement of the piston to perform suction and compression strokes (for example, see German Patent No. 863,751 and British Patent No. 430,830).
The conventionally proposed principle of the compressing mechanism will be described below with reference to FIG. 16.
The compressing mechanism is comprised of a rotary cylinder 101 having a groove 100, and a piston 102 which is slidable within the groove 100. The rotary cylinder 101 is provided for rotation about a point A, and the piston 102 is rotated about a point B.
The movements of the piston and the cylinder will be described as for a case where the rotational radius of the piston 102 is equal to the distance between the center A of rotation of the rotary cylinder 101 and the center B of rotation of the piston 102. When the rotational radius of the piston 102 is larger or smaller than the distance between the rotational center A of the rotary cylinder 101 and the rotational center B of the piston 102, different movements are performed. The description of these different movements is omitted herein.
A broken line C in FIG. 16 indicate a locus for the piston 102. FIGS. 16a to 16i show states in which the piston 102 has been rotated sequentially through every 90 degree.
First, the movement of the piston 102 will be described below.
FIG. 16a shows the state in which the piston 102 lies immediately above the rotational center B. FIG. 16b shows the state in which the piston 102 has been rotated through 90 degree in a counterclockwise direction from the state shown in FIG. 16a. FIG. 16c shows the state in which the piston 102 has been further rotated through 180 degree in the counterclockwise direction from the state shown in FIG. 16a. FIG. 16d shows the state in which the piston 102 has been further rotated through 270 degree in the counterclockwise direction from the state shown in FIG. 16a. FIG. 16e shows the state in which the piston 102 has been rotated through 360 degree in the counterclockwise direction from the state shown in FIG. 16a and has been returned to the state shown in FIG. 16a.
The movement of the rotary cylinder 101 will be described below.
In the state shown in FIG. 16a, the rotary cylinder 101 is located, so that the groove 100 is located vertically. When the piston 102 is moved through 90 degree in the counterclockwise direction from this state, the rotary cylinder 101 is rotated through 45 degree in the counterclockwise direction, as shown in FIG. 16b and hence, the groove 100 is likewise brought into a state in which it is inclined at 45 degree. When the piston 102 is rotated through 180 degree in the counterclockwise direction from the state shown in FIG. 16a, the rotary cylinder 101 is rotated through 90 degree in the counterclockwise direction, as shown in FIG. 16c and hence, the groove 100 is likewise brought into a state in which it is inclined at 90 degree.
In this way, the rotary cylinder 101 is rotated in the same direction with the rotation of the piston 102, but while the piston 102 is rotated through 360 degree, the rotary cylinder 101 is rotated through 180 degree. Therefore, to rotate the rotary cylinder 101 through 360 degree, it is necessary to rotate the piston 102 through 720 degree.
The change in volume of the groove 100 defining the compressing space will be described below.
In the state shown in FIG. 16a, the piston 102 lies at one end in the groove 100 and hence, only one space exists. This space is called a first space 100a herein. In the state shown in FIG. 16b, the first space 100a is narrower, but a second space 100b is produced on the opposite side of the piston 102. In the state shown in FIG. 16c, the first space 100a is further decreased into a size as small as half of the space in the state shown in FIG. 16a, but a second space 100b is of the same size as the first space 100a. The first space 100a is gradually decreased, as shown in FIG. 16d, and is zero in volume in the state shown in FIG. 16e in which the piston 102 has been rotated through 360 degree.
In this way, the first and second spaces 100a and 100b are defined in the groove 100 by the piston 102 and repeatedly varied in volume from the minimum to the maximum and from the maximum to the minimum, whenever the piston 102 is rotated through 360 degree.
Therefore, the spaces defining the compressing chambers perform the compression and suction strokes by the rotation of the piston 102 through 720 degree.
When the compressing mechanism is provided in the casing or bearing and operated, the compressing chambers are defined, so that they are surrounded by the outer peripheral surface of the piston, the wall surface of the groove in the rotary cylinder and end faces of the bearing. The surfaces of respective members defining the compressing chambers are slid on the opposed surfaces. The clearance between the slide faces is set at a small value in order to suppress the leakage of a refrigerant gas in the compressing course to the minimum, and a lubricating oil is supplied into the clearance in order to provide a lubricating effect and a sealing effect.
In such case, when two faces are rotationally slid on each other with the lubricating oil present therebetween, such as the end face of the rotary cylinder and the end face of the bearing, or the end face of the piston and the end face of the bearing, a power loss is produced due to the viscosity of the lubricating oil.
The power loss Ws due to the viscosity is represented by the following equation: EQU Ws=.pi..mu..omega..sup.2 (r.sub.2.sup.4 -r.sub.1.sup.4)/(2.delta.)
wherein .mu. is a viscosity coefficient of the oil; .omega. is a rotational angular speed; r.sub.2 is an outside diameter of the slide face; r.sub.1 is an inside diameter of the slide face; and .delta. is a distance between the slide faces. Thus, the loss Ws due to the viscosity assumes a larger value in proportion to the fourth power of the radius of the slide face.
On the other hand, the power loss Wr produced due to viscosity between the slide faces of the outer peripheral surface of the rotary cylinder and the inner peripheral surface of the casing is represented by the following equation: EQU Wr=2.pi..mu..omega..sup.2 R.sup.3 W/.delta.
wherein R is an outside diameter of the rotary cylinder; and W is a width of the rotary cylinder. The power loss Wr assumes a value proportional to the product of the third power of the outside diameter of the rotary cylinder and the width of the rotary cylinder.